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Publications (7)0 Total impact

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    ABSTRACT: Accurate estimation of the doubly selective mobile radio channels is essential to achieve satisfactory performance in wideband wireless communication systems like 3GPP LTE. Pilot Assisted Channel Estimation (PACE) techniques like Linear Minimum Mean Squared Error (LMMSE), Least Square (LS) etc. are used to estimate the channel states at a certain time-frequency grid specified by the pilot symbols. A model like Basis Expansion Model (BEM) is used to track the doubly selective channel in time between the pilot symbols. BEM performance is sensitive to the PACE results. Imperfections in the PACE results are inevitable due to Inter Carrier Interference (ICI) at high speeds, changing signal to noise ratio (SNR) of the system and mismatch in the parameter values used in PACE calculations. We are able to reduce the effect of such imperfections by shaping the noise at the high frequencies in extended Fixed CE-BEM. Simulations show a decrease in MSE by a factor of ≈2 when the LMMSE results, obtained at 0dB SNR, are used to track the doubly selective channel at 350 km/h.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on; 01/2012
  • M. Petit, A. Springer
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    ABSTRACT: To meet the growing requirements for advanced wireless communications systems, a high flexibility of all subsystems is necessary. In order to keep costs low the specifications for the analog components can be reduced, if the compensation of the resulting impairments is done by digital signal processing. An example for such impairments are slight differences between the I- and Q-branch low pass filters due to production tolerances in direct-conversion receivers that lead to frequency selective I/Q imbalance. A waveform independent digital compensation approach based on second order statistics shows the desired flexibility. Without the knowledge of any transmit data the I/Q mismatch can be compensated by adaptive filtering. This is done by the restoration of a statistical property, called properness, which has been disturbed by the I/Q mismatch. It is shown, that for LTE standard compliant transmission signals under real world conditions the algorithm is ideally suited in terms of performance and hardware implementation. In a fix-point implementation the approach provides a normalized mean square error of below-60 dB, compared to the floating-point simulation.
    Signal Processing Systems (SiPS), 2012 IEEE Workshop on; 01/2012
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    ABSTRACT: The Basis Expansion Model (BEM) is often employed to track the time variant multipath channels. Using an accurate estimation of the Doppler spread for the BEM gives better channel tracking performance for very high speed vehicles (1). We propose a modification of the conventional BEM for 3GPP LTE systems which is independent from the Doppler spread for all realistic speeds. It shows no significant loss of estimation accuracy compared to conventional BEM, thus providing a robust channel tracking for mobile equipment under changing multipath environment with the additional advantage of very low computational complexity. Simulation results of Mean Squared Error (MSE) are provided to support our claim.
    01/2011;
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    ABSTRACT: In direct conversion receivers differences of the analog components in the I- and the Q-branch lead to I/Q mismatch. Digital signal processing can be used to reduce the specification for the RF circuitry. In this paper we focus on the compensation of frequency dependent I/Q mismatch due to different cut-off frequencies of the lowpass filters. This mismatch, which is an issue due to the wide bandwidth used e. g. in LTE systems, is compensated with a second order statistic-based approach. The blind adaptive algorithm recovers a property of complex signals, called properness which is disturbed by the I/Q mismatch. The algorithm achieves a very good performance even with a mismatched upconversion stage. It is able to compensate cut-off differences higher than 10% and is independent of special pilot structures and Rayleigh fading channels.
    Wireless Conference 2011 - Sustainable Wireless Technologies (European Wireless), 11th European; 01/2011
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    ABSTRACT: We presented a precompensation method for a direct up conversion transmitter, where IQM impairments are compensated to achieve optimum results. Measurement results have shown that the proposed model is able to compensate for the TX impairments as well as the amplifier nonlinearities.
    01/2010;
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    ABSTRACT: Noise represents a major performance limiting factor for wireless communication systems. Pre-and post processing of the transmitted information enables to reduce the influence of noise significantly, leading to a severe performance gain. We apply the derivation of an optimal pre-and post processing to a single carrier system with frequency domain equalization (SC/FDE). Comparisons between the standard SC/FDE system with a zero-forcing equalizer and the enhanced system show a performance gain of up to 8 dB at a bit error rate of 10<sup>-5</sup>.
    Wireless Technologies, 2007 European Conference on; 11/2007
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    ABSTRACT: We investigate advantageous data structures of a single carrier system with frequency domain equalization (SC/FDE) for channel estimation and synchronisation. The concept of the SC/FDE system is based on a cyclic prefix - comparable to OFDM (orthogonal frequency division multiplexing). Three equivalent data structures for the SC/FDE system are given, based either on the well known cyclic prefix or on the use of a known symbol sequence - a so-called unique word (UW). We elaborate on the advantages that result for channel estimation and synchronisation.
    Personal Mobile Communications Conference, 2003. 5th European (Conf. Publ. No. 492); 05/2003